Empirical Calibration of the Near-IR Ca II Triplet
The Stellar Library
We have observed a new stellar library of 706 stars at the near-infrared spectral region (from 8348 Å to 9020 Å) with a resolution of 1.5 Å (FWHM). It includes 421 of the 424 stars with known atmospheric parameters of the Lick/IDS Library (Burstein et al. 1984; Faber et al. 1985; Burstein, Faber & González 1986; Gorgas et al. 1993; Worthey et al. 1994). In order to obtain a large sample of stars in common with other previous works devoted to the Ca II triplet, our stellar library was enlarged to include 105 of the 106 stars of Díaz, Terlevich & Terlevich (1989) and 43 of the 55 stars of the sample of Idiart, Thévenin & de Freitas (1997). Moreover, with the aim of filling gaps in the parameter space, we also included stars from several other compilations, mainly focusing on O, B and A types (37 hot stars from the sample of Andrillat, Jaschek & Jaschek 1995), late M types, metal poor, metal rich and chemically peculiar stars (40 stars from a list kindly provided by G. Worthey, private communication, and 102 stars from Jones 1997). Finally, 29 additional stars with high or low Ca/Fe ratios from the catalogue by Thévenin (1998) were also included. The library spans a wide range in spectral types and luminosity classes. Most of them (550) are field stars from the solar neighbourhood, but stars covering a wide range in age (from open clusters) and with different metallicities (from galactic globular clusters) are also included.
The animation shown in the Home page illustrates a sequence of spectral types made with a representative subsample of stars of the near-IR library. Also, the strongest spectral features are indicated in the figure below: the Paschen Series (from P11 to P20), the Ca II triplet (Ca1, Ca2 and Ca3), several metallic lines (Fe I, Mg I and Ti I), molecular bands (TiO and VO) and telluric absorptions.
Early spectral types (O, B and A) are mainly dominated by an apparent H Paschen series which contaminates the Ca II triplet and gradually disappears as the effective temperature decreases. Then, for lower temperatures (G - early M types), the Ca II triplet is the most relevant feature in the near-IR spectral range. Finally, the presence of strong molecular bands (e.g. TiO and VO) in the spectra of the coldest stars (mid - late M types) causes the slope of the local continuum to be steeper, at the same time as the Ca II strength reaches almost negligible values.
Compressed tar files with the spectra of the whole stellar library and their associated error spectra can be downloaded below. See also the available Database for full information and individual spectra of each star.